Precious metal electrical resistance wires



PRECIOU METAL ELECTRICAL RESISTANCE WIRES Eugene Colin, White Plains, and Arthur Jerome Abrams, Harrison, N. Y., assignors to Secon Metals Corporation, White Plains, N. Y.

No Drawing. Application September 29, 1954 Serial No. 459,216

8 Claims. (Cl. 75-172) This invention relates to precious metal alloys and particularly to precious metal electrical resistance wire. in this specification and claims all parts and percentages are on a weight basis.

For uses in which corrosive atmospheres at elevated temperatures are encountered and particularly in the electrical telemetering art and other fields involving the use of rheostats or potentiometers exposed to such atmospheres, base metal alloy resistance wire cannot be used because they oxidize readily with consequent change in the resistance of the wire. Accordingly it is common practice to employ precious metal alloys for the winding, and usually also for the brush or sliding contact of rheostats and potentiometers employed in these fields. Thus, for example, in jet propelled aircraft, computers and in other fields where space is limited, ventilation is inadequate to maintain low temperatures, or corrosive conditions are encountered due, for example, to sulphur hearing atmospheres, salt water containing atmospheres, etc., it is common practice to employ precious metal alloy resistance wire both for the windings and the brushes or sliding contacts of variable resistors employed therein. One type of brush or contact commonly employed is made of a precious metal alloy known as Paliney No. 7 which is now manufactured by the J. M. Ney Company of Hartford, Connecticut, which alloy is believed to consistor" about 35% palladium, platinum, 30% silver, copper and 10% gold. There is now a need for a precious metal alloy resistance wire compatible with Paliney No. 7 and having a specific resistance within the range of 380 to 420 ohms per C. M. F. (circular mill toot).

it is among the objects of this invention to provide precious metal alloys from which electrical resistance wire may be produced which alloys have the following properties:

. (1) Are resistant to oxidization, including oxidization at elevated temperatures as high as 250 C.

(2) Are resistant to corrosion by sulphur bearing atmospheres and salt water containing atmospheres over a wide range of temperatures including temperatures as high as 250 C.

(3) Have a specific resistance within the range of 380 to 420 ohms per C. M. F.

(4) Are electrically stable, i. e., the resistance remains substantially constant and does not change materially with the passage of time.

(5) Have a high tensile strength, at least 300,000 lbs. per square inch for Wire having a diameter of 0.001 inch.

(6) Have a low temperature coefiicient of resistance; viz. below 0.00024.

(7) Wire made from these alloys are homogeneous, can be worked readily, i. e., wound readily without breaking even in the case of small diameter wire of the order of 0.001 and less inches in diameter, and do not age harden materially.

(8) Are compatible with Paliney No. 7 brushes or sliding contacts, so much so that the resultant assembly "ice has an exceptional low noise level and an exceedingly long life.

Still another object of this invention is to provide electrical resistance wire having the desirable qualities above noted and which when wound to produce a variable resistor, operates at a relatively low noise level, i. e., the contact resistance at the interface between the brush and the wire winding remains constant and is of a relative low order of magnitude so that the reistance Wire is admirably suited to produce variable resistors including potentiometers of the low torque and ultra low torque types.

The alloy of this invention consists of from 54 to 60, preferably from 56 to 58 parts of platinum, from 34 to 40, preferably from 36 to 38 parts of palladium, and from 5 to 8 parts of molybdenum or of a mixture of molybdenum and tungsten containing not more than 25% tungsten, i. e., not more than one quarter of this mixture is tungsten, the rest being molybdenum. The platinum, palladium, molybdenum and tungsten, if used, may contain traces of impurities usually present in the production of these metals. Furthermore the alloy may be produced by a process of melting the platinum, palladium, molybdenum and tungsten, if used, in the proportions above indicated, and adding a deoxidizer such'for example as manganese, thorium, zirconium, titanium, or aluminum or a mixture of such deoxidizers to the melt. While the amount of the deoxidizer thus added is small, usually not exceeding about 0.3% of the total mixture and most if not all of the deoxidizer is removed with the slag separated from the molten metal, small amounts of the deoxidizer may remain in the alloy. Accordingly, it will be understo d that Where in the claims reference is made to platinum, palladium, molybdenum or tungsten, the claims include not only the pure metals, but also these metals containing traces of impurities and/or small amounts of deoxidizer which may have been employed in the production of the alloy. Furthermore, the invention is not limited to the production of the alloy by a hot melting technique,

but includes the alloys, and resistance wire made therefrom, by a powder metallurgical technique.

In the production of an electrical resistance wire, an ingot of the alloy is first produced either by a hot melt or powder metallurgical technique. This ingot is then reduced in size to produce a rod of relatively small diameter which is then drawn with intermediate annealing treatments between drawings to produce a wire of the desired diameter. As the drawing technique employed may be any conventional type and as such forms no part of this invention, further description thereof is believed unnecessary. The wire thus produced has a diameter of from 0.00025 to 0.005, preferably from 0.0007 to 0.002 inch. It may be bare or enamelled.

The following table gives the more important desirable proportions of several exemplary electrical resistance wires embodying this invention:

Table Specific re- Tensile strength Composition of resistsistance in Temperature in lbs. per sq. in. once wire, percent by ohms per coefficient of for Wire having weight 0. M. I". resistance a die. of 0.001

22 0. inch 57% platinum- 37% palladium 400 0.00021 325,000 6% molybdenum 3 5 ii lt 7 pa a um 1%tungsten u 385 0. 00024 315, 000 5% molybdenum 59.75% platinum. 34.0% palladium--- 380 0.00024 310, 000 6.25% molybdenum.

Each of the above described resistance wires is resistant to corrosion including corrosion by sulphur bearing atmospheres, salt water containing atmospheres at elevated temperatures as high as 250 C. and resistant to oxidation including oxidation at such elevated temperatures. These wires are eminently suited for use in the production of variable resistors. In such uses corrosion at the interface between the wire and the brush or other sliding contact does not take place, and the wire has and retains a smooth surface for the brush or contact to wipe thereacross with consequent low brush or contact pressure required for such movement. The wire even in small sizes as low as 0.00025 inch in diameter, is readily and easily wound and otherwise worked, does not age harden, is uniform, homogeneous and electrically stable, i. e., the resistance remains constant with the passage of time. When used as a winding for a potentiometer and with a proper brush including brushes of Paliney No. 7, the wire results in a construction having an exceptional low noise level,

and an exceedingly long life, at least 1,000,000 cycles.

From the foregoing it will be evident that this invention provides new alloys eminently satisfactory for use in producing electrical resistance wire, which wire combines to an exceptional and unusual extent the properties of (a) specific resistance Within the range of 380 to 420 ohms per C. M. R; ([2) low temperature coefficient of resistance; (c) high tensile strength for relatively small diameter wire; and (d) unusually good compatibility with Paliney No. 7 as the brush or sliding contact when the wire is used as the winding of a variable resistor including potentiometers. Furthermore, the wire can readily and easily be fabricated even in the case of the very small size wire, i. e., wire having a diameter of 0.00025 to 0.005 inch. The resistance wire is electrically stable, resists oxidation and corrosion includ ing corrosion by sulphur bearing and/ or salt Water containg atmospheres at elevated temperatures.

Since different embodiments of this invention can be made without departing from its scope, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. An electrical resistance wire constituted of a precious metal alloy consisting of from 54 to 60 parts of platinum, 34 to 40 parts of palladium and from to 8 parts of metal from the group consisting of molybdenum and a mixture of molybdenum and tungsten, which mixture contains not more than of tungsten.

2. An electrical resistance wire constituted of a precious metal alloy consisting of 56 to 58 parts of platinum,

4 36 to 38 parts of palladium and 5 to 8 parts of molybdenum.

3. An electrical resistance wire having a diameter of from 0.00025 to 0.005 inch and consisting of a precious metal-alloy consisting of from 54 to parts of platinum, 34 to 40 parts of palladium and from 5 to 8 parts of metal from the group consisting of molybdenum and a mixture of molybdenum and tungsten, which mixture contains not more than 25% of tungsten.

4. An electrical resistance wire having a diameter of from 0.00025 to 0.005 inch and constituted of a precious metal alloy consisting of from 56 to 58 parts of platinum, 36 to 38 parts of palladium and 5 to 8 parts of mo1ybdenum.

5. An electrical resistance wire having a diameter of from 0.0007 to 0.002 inch, and consisting of a precious metal alloy consisting of from 54 to 60 parts of platinum, 34 to 40 parts of palladium and from 5 to 8 parts of metal from the group consisting of molybdenum and a mixture of molybdenum and tungsten, which mixture contains not more than 25% of tungsten.

6. An electrical resistance wire having a diameter of from 0.0007 to 0.002 inch and constituted of a precious metal alloy consisting of 57% platinum, 37% palladium and 6% molybdenum.

7. An electrical resistance wire having a diameter of from 0.0007 to 0.002 inch, and constituted of a precious metal alloy consisting of 57% platinum, 37% palladium, 1% tungsten and 5% molybdenum.

8. An electrical resistance wire having a diameter of from 0.0007'to 0.002 inch, and constituted of a precious metal alloy consisting of 59.75% platinum, 34% palladium and 6.25% molybdenum.

References Cited in the file of this patent UNITED STATES PATENTS 1,407,525 Fry Feb. 21, 1922 1,695,044 Hallmann Dec. 11, 1928 1,779,603 Kingsbury Oct. 28, 1930 2,391,455 Hensel Dec. 25, 1945 2,537,733 Brenner Jan. 9, 1951 2,696,544 Poch Dec. 7, 1954 FOREIGN PATENTS 565,807 Great Britain Nov. 29, 1944 OTHER REFERENCES Modern Uses of Nonferrous Metals (Wise), 2nd ed. (1953), published by AIME (New York) (pages 290-292 relied on). 

1. AN ELECTRICAL RESISTANCE WIRE CONSTITUTED OF A PRECIOUS METAL ALLOY CONSISTING OF FROM 54 TO 60 PARTS OF PLATINUM, 34 TO 40 PARTS OF PALLADIUM AND FROM 5 TO 8 PARTS OF METAL FROM THE GROUP CONSISTING OF MOLYBDENUM AND A MIXTURE OF MOLYBDENUM AND TUNGSTEN, WHICH MIXTURE CONTAINS NOT MORE THAN 25% OF TUNGSTEN. 